Rechargeable lithium battery

ABSTRACT

A rechargeable lithium battery includes an electrode laminate including a positive electrode including a positive current collector and a positive active material layer disposed on the positive current collector; a negative electrode including a negative current collector, a negative active material layer disposed on the negative current collector, and a negative electrode functional layer disposed on the negative active material layer; and a separator, wherein the electrode laminate has a ratio (L/W) of a height (L), which is a length in a protruding direction of an electrode terminal, relative to a width (W), which is perpendicular to the protruding direction of the electrode terminal and parallel to the laminate surface, is about 1.1 to about 2.3, the positive active material layer includes a first positive active material including at least one of a composite oxide of a metal selected from cobalt, manganese, nickel, and a combination thereof and lithium and a second positive active material including a compound represented by Chemical Formula 1, the negative electrode functional layer includes flake-shaped polyethylene particles, and an operation voltage is greater than or equal to about 4.3 V. 
       Li a Fe 1-x1 M x1 PO 4    [Chemical Formula 1]
         In Chemical Formula 1, 0.90≤a≤1.8, 0≤x1≤0.7, and M is Mn, Co, Ni, or a combination thereof.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from and the benefit of Korean PatentApplication No. 10-2019-0052570 filed on May 3, 2019, which is herebyincorporated by reference for all purposes as if fully set forth herein.Further, two related co-pending applications were filed on Jul. 2, 2019with United States Patent and Trademark Office, as U.S. patentapplication Ser., No. 16/460,765 and U.S. patent application Ser. No.16/460,779, both of which are hereby incorporated by reference for allpurposes as if fully set forth herein, but are not admitted to be priorart with respect to the present invention by their mention in thecross-reference section. su

BACKGROUND Field

Exemplary embodiments/implementations of the invention relate generallyto a rechargeable lithium battery.

Discussion of the Background

A portable information device such as a cell phone, a laptop, smartphone, and the like or an electric vehicle has used a rechargeablelithium battery having high energy density and easy portability as adriving power source. In addition, research on use of a rechargeablelithium battery as a power source for a hybrid or electric vehicle or apower storage by using high energy density characteristics has recentlybeen actively made.

One of the main research tasks of such a rechargeable lithium battery isto improve the safety of the rechargeable battery. For example, if therechargeable lithium battery is exothermic due to internal shortcircuit, overcharge and overdischarge, and the like, and an electrolytedecomposition reaction and thermal runaway phenomenon occur, an internalpressure inside the battery may rise rapidly to cause battery explosion.Among these, when the internal short circuit of the rechargeable lithiumbattery occurs, there is a high risk of explosion because the highelectrical energy stored in each electrode is conducted in the shortedpositive electrode and negative electrode.

In addition to the damage of the rechargeable lithium battery, theexplosion may cause fatal damages to the user. Therefore, it is urgentto improve stability of the rechargeable lithium battery.

On the other hand, Lithium Iron Phosphate (LFP) is used as a lowheat-generating safety material, but an average potential thereof isrelatively low, accompanied by a decrease in capacity when discharging.Therefore, there is a need for technology development to improve theseproblems.

The above information disclosed in this Background section is only forunderstanding of the background of the inventive concepts, and,therefore, it may contain information that does not constitute priorart.

SUMMARY

Devices constructed/methods according to exemplary implementationsembodiments of the invention are capable of being operated at highvoltage and having high capacity and high stability.

According to one or more implementations/embodiments of the invention, alithium battery includes a rechargeable an electrode laminate includinga positive electrode including a positive current collector and apositive active material layer disposed on the positive currentcollector; a negative electrode including a negative current collector,a negative active material layer disposed on the negative currentcollector, and a negative electrode functional layer disposed on thenegative active material layer; and a separator, wherein the electrodelaminate has a ratio (L/W) of a height (L), which is a length in aprotruding direction of an electrode terminal, relative to a width (W),which is perpendicular to the protruding direction of the electrodeterminal and parallel to the laminate surface, is about 1.1 to about2.3, the positive active material layer includes a first positive activematerial including at least one of a composite oxide of a metal selectedfrom cobalt, manganese, nickel, and a combination thereof and lithiumand a second positive active material including a compound representedby Chemical Formula 1, the negative electrode functional layer includesflake-shaped polyethylene particles, and an operation voltage is greaterthan or equal to about 4.3 V.

Li_(a)Fe_(1-x1)M_(x1)PO₄   [Chemical Formula 1]

In Chemical Formula 1, 0.90 <a <1.8, 0 <xl <0.7, and M is Mn, Co, Ni, ora combination thereof.

Safety may be achieved by implementing an early shut-down function as arechargeable lithium battery that may operate at high voltages withoutdegradation of capacity.

Additional features of the inventive concepts will be set forth in thedescription which follows, and in part will be apparent from thedescription, or may be learned by practice of the inventive concepts.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate exemplary embodiments of theinvention, and together with the description serve to explain theinventive concepts.

FIG. 1 schematically shows a structure of a rechargeable lithium batteryaccording to an embodiment of the present disclosure.

FIG. 2 is a schematic view of an electrode laminate according to anembodiment of the present disclosure.

FIG. 3 shows heat transfer simulation results over time duringpenetration safety evaluation for the rechargeable lithium battery cellsaccording to Examples 1 and 2 of the present disclosure.

FIG. 4 shows heat transfer simulation results over time duringpenetration safety evaluation for the rechargeable lithium battery cellsaccording to Comparative Examples 1 and 2.

FIG. 5 is a SEM photograph of polyethylene particles of a negativeelectrode functional layer according to an embodiment.

FIG. 6 is a SEM photograph of a negative electrode composition accordingto an embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following description, for the purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of various exemplary embodiments or implementations of theinvention. As used herein “embodiments” and “implementations” areinterchangeable words that are non-limiting examples of devices ormethods employing one or more of the inventive concepts disclosedherein. It is apparent, however, that various exemplary embodiments maybe practiced without these specific details or with one or moreequivalent arrangements. In other instances, well-known structures anddevices are shown in block diagram form in order to avoid unnecessarilyobscuring various exemplary embodiments. Further, various exemplaryembodiments may be different, but do not have to be exclusive. Forexample, specific shapes, configurations, and characteristics of anexemplary embodiment may be used or implemented in another exemplaryembodiment without departing from the inventive concepts.

Unless otherwise specified, the illustrated exemplary embodiments are tobe understood as providing exemplary features of varying detail of someways in which the inventive concepts may be implemented in practice.Therefore, unless otherwise specified, the features, components,modules, layers, films, panels, regions, and/or aspects, etc.(hereinafter individually or collectively referred to as “elements”), ofthe various embodiments may be otherwise combined, separated,interchanged, and/or rearranged without departing from the inventiveconcepts.

The use of cross-hatching and/or shading in the accompanying drawings isgenerally provided to clarify boundaries between adjacent elements. Assuch, neither the presence nor the absence of cross-hatching or shadingconveys or indicates any preference or requirement for particularmaterials, material properties, dimensions, proportions, commonalitiesbetween illustrated elements, and/or any other characteristic,attribute, property, etc., of the elements, unless specified. Further,in the accompanying drawings, the size and relative sizes of elementsmay be exaggerated for clarity and/or descriptive purposes. When anexemplary embodiment may be implemented differently, a specific processorder may be performed differently from the described order. Forexample, two consecutively described processes may be performedsubstantially at the same time or performed in an order opposite to thedescribed order. Also, like reference numerals denote like elements.

When an element, such as a layer, is referred to as being “on,”“connected to,” or “coupled to” another element or layer, it may bedirectly on, connected to, or coupled to the other element or layer orintervening elements or layers may be present. When, however, an elementor layer is referred to as being “directly on,” “directly connected to,”or “directly coupled to” another element or layer, there are nointervening elements or layers present. To this end, the term“connected” may refer to physical, electrical, and/or fluid connection,with or without intervening elements. Further, the D1-axis, the D2-axis,and the D3-axis are not limited to three axes of a rectangularcoordinate system, such as the x, y, and z-axes, and may be interpretedin a broader sense. For example, the D1-axis, the D2-axis, and theD3-axis may be perpendicular to one another, or may represent differentdirections that are not perpendicular to one another. For the purposesof this disclosure, “at least one of X, Y, and Z” and “at least oneselected from the group consisting of X, Y, and Z” may be construed as Xonly, Y only, Z only, or any combination of two or more of X, Y, and Z,such as, for instance, XYZ, XYY, YZ, and ZZ. As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items.

Although the terms “first,” “second,” etc. may be used herein todescribe various types of elements, these elements should not be limitedby these terms. These terms are used to distinguish one element fromanother element. Thus, a first element discussed below could be termed asecond element without departing from the teachings of the disclosure.

Spatially relative terms, such as “beneath,” “below,” “under,” “lower,”“above,” “upper,” “over,” “higher,” “side” (e.g., as in “sidewall”), andthe like, may be used herein for descriptive purposes, and, thereby, todescribe one elements relationship to another element(s) as illustratedin the drawings. Spatially relative terms are intended to encompassdifferent orientations of an apparatus in use, operation, and/ormanufacture in addition to the orientation depicted in the drawings. Forexample, if the apparatus in the drawings is turned over, elementsdescribed as “below” or “beneath” other elements or features would thenbe oriented “above” the other elements or features. Thus, the exemplaryterm “below” can encompass both an orientation of above and below.Furthermore, the apparatus may be otherwise oriented (e.g., rotated 90degrees or at other orientations), and, as such, the spatially relativedescriptors used herein interpreted accordingly.

The terminology used herein is for the purpose of describing particularembodiments and is not intended to be limiting. As used herein, thesingular forms, “a,” “an,” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. Moreover,the terms “comprises,” “comprising,” “includes,” and/or “including,”when used in this specification, specify the presence of statedfeatures, integers, steps, operations, elements, components, and/orgroups thereof, but do not preclude the presence or addition of one ormore other features, integers, steps, operations, elements, components,and/or groups thereof. It is also noted that, as used herein, the terms“substantially,” “about,” and other similar terms, are used as terms ofapproximation and not as terms of degree, and, as such, are utilized toaccount for inherent deviations in measured, calculated, and/or providedvalues that would be recognized by one of ordinary skill in the art.

Various exemplary embodiments are described herein with reference tosectional and/or exploded illustrations that are schematic illustrationsof idealized exemplary embodiments and/or intermediate structures. Assuch, variations from the shapes of the illustrations as a result, forexample, of manufacturing techniques and/or tolerances, are to beexpected. Thus, exemplary embodiments disclosed herein should notnecessarily be construed as limited to the particular illustrated shapesof regions, but are to include deviations in shapes that result from,for instance, manufacturing. In this manner, regions illustrated in thedrawings may be schematic in nature and the shapes of these regions maynot reflect actual shapes of regions of a device and, as such, are notnecessarily intended to be limiting.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure is a part. Terms,such as those defined in commonly used dictionaries, should beinterpreted as having a meaning that is consistent with their meaning inthe context of the relevant art and should not be interpreted in anidealized or overly formal sense, unless expressly so defined herein.

Hereinafter, referring to the drawings, embodiments of the presentdisclosure are described in detail. In the following description of thepresent disclosure, the well-known functions or constructions will notbe described in order to clarify the present disclosure.

In order to clearly illustrate the present disclosure, the descriptionand relationships are omitted, and throughout the disclosure, the sameor similar configuration elements are designated by the same referencenumerals. Also, since the size and thickness of each configuration shownin the drawing are arbitrarily shown for better understanding and easeof description, the present disclosure is not necessarily limitedthereto.

A rechargeable lithium battery may be classified into a lithium ionbattery, a lithium ion polymer battery, and a lithium polymer batterydepending on kinds of a separator and an electrolyte. It also may beclassified to be cylindrical, prismatic, coin-type, pouch-type, and thelike depending on shape. In addition, it may be bulk type and thin filmtype depending on sizes. Structures and manufacturing methods forlithium ion batteries pertaining to this disclosure are well known inthe art.

Hereinafter, as an example of a rechargeable lithium battery, apouch-type rechargeable lithium battery is for example described. FIG. 1schematically shows a structure of a rechargeable lithium batteryaccording to an embodiment. Referring to FIG. 1, a rechargeable lithiumbattery 1 according to an embodiment of the present disclosure mayinclude a case 20, an electrode laminate 10 inserted into a case 20, anda positive electrode terminal 40 and a negative electrode terminal 50that are electrically connected to the electrode laminate. The positiveelectrode terminal 40 and the negative electrode terminal 50 may bedrawn out of the case 20 through tabs, respectively, and arerespectively insulated from the case 20 by an insulation member 60.

As shown in FIG. 1, the electrode laminate 10 has a structure in which apositive electrode 11 and a negative electrode 12 of rectangular sheetshapes with predetermined sizes and a separator 13 is disposedtherebetween are laminated and wound in one direction (jelly-roll type).Alternatively, although not shown, a plate-shaped positive electrode, aplate-shaped negative electrode, and a plate-shaped separator havingpredetermined sizes may be laminated, while the positive electrode andthe negative electrode may be formed in a stacked (laminated) structurein which the separator is alternately stacked.

The electrode laminate 10 may include at least one positive electrode,at least one negative electrode, and at least one separator.

The case 20 may include a lower case 22 and an upper case 21, and theelectrode laminate 10 may be accommodated in the inner space 221 of thelower case 22.

After the electrode laminate 10 is put in the case 20, a sealingmaterial is applied to a sealing portion 222 disposed at the edge of thelower case 22 to seal the upper case 21 and the lower case 22.

In addition, the positive electrode 11, the negative electrode 12, andthe separator 13 may be impregnated in the electrolyte.

The positive electrode 11 may include a positive current collector and apositive active material layer formed on the positive current collector.The positive electrode active material layer may include a positiveactive material, a positive electrode binder, and optionally aconductive material.

Hereinafter, a detailed configuration of the rechargeable lithiumbattery 1 according to an embodiment of the present disclosure isdescribed.

The rechargeable lithium battery according to an embodiment of thepresent disclosure includes an electrode laminate including a positiveelectrode, a negative electrode, and a separator and the electrodelaminate has a ratio (L/W) of a height (L), which is a length in aprotruding direction of an electrode terminal, relative to a width (W),which is perpendicular to the protruding direction of the electrodeterminal and parallel to the laminate surface, is about 1.1 to about2.3.

In order to define the width and height of the electrode laminate, aschematic view of the electrode laminate is shown in FIG. 2.

FIG. 2 is a schematic view of an electrode laminate according to anembodiment of the present disclosure.

According to FIG. 2, the width (W) of the electrode laminate means alength perpendicular to a protruding direction of the electrode terminaland parallel to the laminate surface in the packaged electrode laminate.That is, in the packaged electrode laminate, it means the length of asurface in a direction in which the positive electrode, the negativeelectrode and the separator are laminated, and in a directionperpendicular to a protruding direction of the electrode terminal.

In addition, the height (L) of the electrode laminate means a length ofthe protruding direction of an electrode terminal in a packagedelectrode laminate. In this case, a length extended by an electrodeterminal, i.e., a negative electrode terminal and a positive electrodeterminal is excluded.

When the ratio (L/W) of the height relative to the width of theelectrode laminate satisfies 1.1 to 2.3, safety may be ensured whenoperating at a high voltage of greater than or equal to about 4.3 V.

The positive electrode includes a positive electrode current collectorand a positive active material layer disposed on the positive currentcollector, and the positive active material layer includes a firstpositive active material and a second positive active material.

The first positive active material may include at least one of acomposite oxide of a metal selected from cobalt, manganese, nickel, anda combination thereof and lithium and a second positive active materialincluding a compound represented by Chemical Formula 1.

Li_(a)Fe_(1-x1)M_(x1)PO₄   [Chemical Formula 1]

In Chemical Formula 1, 0.90 <a <1.8, 0 <xl <0.7, and M is Mn, Co, Ni, ora combination thereof.

The first positive active material is a high-capacity material havinghigh energy density per unit amount and thus may minimize capacitydeterioration during the operation at a high voltage of greater than orequal to about 4.3 V, and the second positive active material is a lowheat-generating stability material and thus may secure stability. Inother words, the first and second positive active materials are usedtogether and thus may realize a high-capacity and high stabilityrechargeable battery.

Particularly, the rechargeable lithium battery according to anembodiment includes a positive electrode including the first positiveactive material and accordingly, may minimize capacity deteriorationduring the operation at a high voltage of greater than or equal to about4.3 V and thus improve cycle-life characteristics.

The first positive active material may be included in a weight of about80 wt % to about 97 wt %, and specifically about 80 wt % to about 95 wt%, for example about 85 to about 95 wt % or about 85 to about 94 wt %based on a total weight of the positive active material layer.

The positive active material layer may further include a positiveelectrode functional layer disposed on the positive active materiallayer.

For example, the first positive active material may be included in thepositive active material layer and the second positive active materialmay be included in the positive electrode functional layer.

In this case, the first positive active material and the second positiveactive material may be included in a weight ratio of about 97:3 to about80:20 or a weight ratio of about 95:5 to about 80:20.

For example, the first positive active material may be included in thepositive active material layer, and the second positive active materialmay be included in the positive active material layer and the positiveelectrode functional layer, respectively.

In this case, the first positive active material and the second positiveactive material may be included in a weight ratio of about 94:6 to about85:15.

In this case, the second positive active material of the positiveelectrode functional layer may be included in about 20 parts by weightto about 120 parts by weight based on 100 parts by weight of the secondpositive active material of the positive active material layer.

When the first positive active material and the second positive activematerial satisfy the above ranges, high capacity and safety may besecured.

The first positive active material may specifically include one ofLiCoO₂, Li_(b)M¹ _(1-y1-z1)M² _(y1)M³ _(z1)O₂(0.9≤b≤1.8, 0≤y1≤1, 0≤z1≤1,0≤y1+z1≤1, M¹, M², and M³ are independently a metal of Ni, Co, Mn, Al,Sr, Mg, or La), and a combination thereof.

For example, the first positive active material may include LiCoO₂, butis not limited thereto.

For example, M¹ may be Ni, and M² and M³ may independently be a metalsuch as Co, Mn, Al, Sr, Mg, or La.

More specifically, M¹ may be Ni, M² may be Co, and M³ may be Mn or Al,but are not limited thereto.

The second positive active material may include LiFePO₄.

The negative electrode may include a negative current collector, anegative active material layer disposed on the negative currentcollector, and a negative electrode functional layer disposed on thenegative active material layer, and the negative electrode functionallayer may include flake-shaped polyethylene particles.

When the flake-shaped polyethylene particles are used, a large area maybe effectively blocked at a shut-down temperature, compared withspherical shape polyethylene particles. Accordingly, the negativeelectrode having the negative electrode functional layer including theflake-shaped polyethylene particles may also be included to moreeffectively implement the shut-down function and thus prevent anadditional chemical reaction. This improves a rechargeable batterysafety.

The polyethylene is generally HDPE (high density polyethylene, density:about 0.94 g/cc to about 0.965 g/cc), MDPE (medium density polyethylene,density: about 0.925 g/cc to about 0.94 g/cc), LDPE (low densitypolyethylene, density: about 0.91 g/cc to about 0.925 g/cc), VLDPE (verylow density polyethylene, density: about 0.85 g/cc to about 0.91 g/cc),and the like.

The flake-shaped polyethylene particles may be used alone or incombination of two or more polyethylene polymers such as HDPE, MDPE, orLDPE.

The average particle size (D50) of the flake-shaped polyethyleneparticles included in the negative electrode functional layer disposedon the negative active material layer may be about 1 μm to about 8 μm,and specifically about 2 μm to about 6 μm.

As used herein, when a definition is not otherwise provided, the averageparticle size (D50) may be measured by a method well-known to a personof ordinary skill in the art, for example, as a particle size analyzer,or from TEM or SEM photographs. Alternatively, a dynamiclight-scattering measurement device is used to perform a data analysis,and the number of particles is counted for each particle size range.From this, the D50 value may be easily obtained through a calculation.

More precisely, the particle size of a flake-shaped polyethyleneparticle may be determined by a dynamic light-scattering measurementmethod. Specifically, the size may be measured by ISO 13320 through theanalysis of the light-scattering properties of the particles. For thenon-spherical particles, a size distribution is reported, where thepredicted scattering pattern for the volumetric sum of sphericalparticles matches the measured scattering pattern.

For example, the D50 is also known as the median diameter or the mediumvalue of the particle size distribution, it is the value of the particlediameter at 50% in the cumulative distribution.

On the other hand, a ratio of the long axis length relative to the shortaxis length of the flake-shaped polyethylene particles may be about 1 toabout 5, specifically about 1.1 to about 4.5, for example about 1.2 toabout 3.5.

In addition, a thickness of the flake-shaped polyethylene particles maybe about 0.2 μm to about 4 μm, specifically, about 0.3 μm to about 2.5μm, for example may be about 0.3 μm to about 1.5 μm.

The polyethylene particles according to this disclosure areflake-shaped, as seen in FIG. 5, and the average particle size may bedefined as (D50) described above.

When the size and thickness of the flake-shaped polyethylene particlesare within the above range, ion channels may be effectively closed evenin a small amount.

When the negative electrode functional layer including the flake-shapedpolyethylene particles is provided, a reaction rate may be increasedaccording to temperature under the same reaction conditions, comparedwith the case of including spherical polyethylene particles, therebyimproving stability of the rechargeable lithium battery. In the case ofthe flake-shaped polyethylene particles before melting, an area coveringpores is thinner and wider than that of the spherical shape polyethyleneparticles before melting. When the polyethylene particles are melted ata predetermined temperature or more to close ion channels, a reactionrate is faster because the flake-shaped polyethylene particles have alarger area than that of the electrode plate closed by the meltedspherical polyethylene particles.

That is, the polyethylene particles included in the negative electrodefunctional layer during thermal runaway of the battery is melted toclose the ion channels, thereby limiting the movement of the ions toprevent additional electrochemical reactions by a shut-down function.

For example, as shown in FIG. 6, since the flake-shaped polyethyleneparticles according to the embodiment are disposed in a thin and wideshape on the pores in a composition for the negative electrodefunctional layer, the flake-shaped polyethylene particles melts morerapidly during thermal runaway due to thermal/physical impact, therebysuppressing passage of ions.

On the other hand, the electrode laminate may have a volume of about17.5 cc to about 30 cc but depending on uses, be manufactured into aunit cell having a volume of greater than or equal to about 30 cc.

In addition, the electrode laminate may have energy density of about 600Wh/L to about 750 Wh/L.

The energy density corresponds to capacity of a rechargeable battery andmay be obtained by dividing energy (Wh) of the rechargeable batteryunder a standard charge and discharge condition (e.g., charge at 0.5C/discharge at 0.2 C) by a volume (L) of the rechargeable battery andthen, standardizing the quotient.

For example, the energy density of the electrode laminate may be in arange of about 630 Wh/L to about 720 Wh/L or about 650 Wh/L to about 690Wh/L.

The rechargeable battery according to an embodiment includes anelectrode laminate having energy density within the range and thus mayrealize a high voltage and high capacity.

The rechargeable battery according to an embodiment for example may havean operation voltage of about 4.3 V to about 4.5 V.

The positive active material layer may optionally further include apositive electrode conductive material and a positive electrode binder.

The amount of the positive electrode conductive material and thepositive electrode binder may be about 1 wt % to about 7 wt % based on atotal weight of the positive active material layer, respectively.

The positive electrode conductive material is used to impartconductivity to the positive electrode, and may be used as long as it isan electron conductive material without causing chemical change in thebattery. Examples of the conductive material may include a carbon-basedmaterial such as natural graphite, artificial graphite, carbon black,acetylene black, ketjen black, a carbon fiber, and the like; ametal-based material of a metal powder or a metal fiber includingcopper, nickel, aluminum, silver, and the like; a conductive polymersuch as a polyphenylene derivative; or a mixture thereof.

The positive electrode binder adheres positively to positive activematerial particles, and also serves to adhere positive active materialsto a current collector well. Examples thereof may be polyvinyl alcohol,carboxylmethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose,polyvinylchloride, carboxylated polyvinylchloride, polyvinylfluoride, anethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane,polytetrafluoroethylene, polyvinylidene fluoride, polyethylene,polypropylene, a styrene-butadiene rubber, an acrylatedstyrene-butadiene rubber, an epoxy resin, nylon, and the like, but arenot limited thereto.

As the positive current collector, aluminum, nickel, and the like may beused, but is not limited thereto.

The electrolyte includes a non-aqueous organic solvent and a lithiumsalt.

The non-aqueous organic solvent serves as a medium for transporting ionstaking part in the electrochemical reaction of a battery.

The non-aqueous organic solvent may include a carbonate-based,ester-based, ether-based, ketone-based, alcohol-based, or aproticsolvent. The carbonate-based solvent may include dimethyl carbonate(DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropylcarbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate(MEC), ethylene carbonate (EC), propylene carbonate (PC), butylenecarbonate (BC), and the like and the ester-based solvent may includemethyl acetate, ethyl acetate, n-propyl acetate, dimethylacetate,methylpropionate, ethylpropionate, γ-butyrolactone, decanolide,valerolactone, mevalonolactone, caprolactone, and the like. Theether-based solvent may include dibutyl ether, tetraglyme, diglyme,dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and the likeand the ketone-based solvent may include cyclohexanone, and the like.The alcohol-based solvent include ethyl alcohol, isopropyl alcohol, andso on, and examples of the aprotic solvent include nitriles such as R—CN(wherein R is a C₂ to C₂₀ linear, branched, or cyclic hydrocarbon groupthat may include a double bond, an aromatic ring, or an ether bond),amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane,sulfolanes, and so on.

The non-aqueous organic solvent may be used alone or in a mixture of twoor more. When the organic solvent is used in a mixture, the mixtureratio can be controlled in accordance with a desirable batteryperformance.

The carbonate-based solvent may include a mixture of a cyclic carbonateand a chain carbonate. The cyclic carbonate and the chain carbonate aremixed together at a volume ratio of about 1:1 to about 1:9, and when themixture is used as an electrolyte, the electrolyte performance may beenhanced.

The non-aqueous organic solvent of the present disclosure may furtherinclude an aromatic hydrocarbon-based organic solvent in addition to thecarbonate-based solvent. In this case, the carbonate-based solvent andthe aromatic hydrocarbon-based organic solvent may be mixed in a volumeratio of about 1:1 to about 30:1.

As the aromatic hydrocarbon-based organic solvent, an aromatichydrocarbon-based compound of Chemical Formula 2 may be used.

In Chemical Formula 2, R₁ to R₆ are the same or different and areselected from hydrogen, a halogen, a C1 to C10 alkyl group, a haloalkylgroup, and a combination thereof.

Specific examples of the aromatic hydrocarbon-based organic solvent maybe selected from benzene, fluorobenzene, 1,2-difluorobenzene,1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene,1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene,1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene,1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene,1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene,1,2,4-triiodobenzene, toluene, fluorotoluene, 2,3-difluorotoluene,2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluorotoluene,2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene,2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene,2,3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene,2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene,2,3,5-triiodotoluene, xylene, and a combination thereof.

The non-aqueous electrolyte may further include vinylene carbonate or anethylene carbonate-based compound of Chemical Formula 3 in order toimprove cycle-life of a battery.

In Chemical Formula 3, R₇ and R₈ may be the same or different and may beselected from hydrogen, a halogen group, a cyano group (CN), a nitrogroup (NO₂), and a fluorinated C1 to C5 alkyl group, wherein at leastone of R₇ and R₈ is selected from a halogen group, a cyano group (CN), anitro group (NO₂), and a fluorinated C1 to C5 alkyl group, provided thatR₇ and R₈ are not both hydrogen.

Examples of the ethylene carbonate-based compound may include difluoroethylenecarbonate, chloroethylene carbonate, dichloroethylene carbonate,bromoethylene carbonate, dibromoethylene carbonate, nitroethylenecarbonate, cyanoethylene carbonate, or fluoroethylene carbonate. Theamount of the cycle-life improvement additive may be used within anappropriate range.

The lithium salt dissolved in an organic solvent supplies a battery withlithium ions, basically operates the rechargeable lithium battery, andimproves transportation of the lithium ions between a positive electrodeand a negative electrode. Examples of the lithium salt include at leastone supporting salt selected from LiPF₆, LiBF₄, LiSbF₆, LiAsF₆,LiN(SO₂C₂F₅)₂, Li(CF₃SO₂)₂N, LiN(SO₃C₂F₅)₂, LiC₄F₉SO₃, LiClO₄, LiAlO₂,LiAlCl₄, LiN(C_(x)F_(2x+1)SO₂)(C_(y)F_(2y+1)SO₂) wherein, x and y arenatural numbers, LiCl, LiI, and LiB(C₂O₄)₂ (lithium bis(oxalato) borate,LiBOB). A concentration of the lithium salt may range from about 0.1 Mto about 2.0 M. When the lithium salt is included at the aboveconcentration range, an electrolyte may have excellent performance andlithium ion mobility due to optimal electrolyte conductivity andviscosity.

The negative electrode functional layer may further include inorganicparticles and a binder.

A sum weight of the flake-shaped polyethylene particles and theinorganic particles: a weight of the binder may be a weight ratio ofabout 80:20 to about 99:1, and specifically, a weight ratio of about85:15 to about 97:3.

The flake-shaped polyethylene particles and the inorganic particles maybe included in a weight ratio of about 95:5 to about 10:90, andspecifically in a weight ratio of about 70:30 to about 30:70.

The amounts of the flake-shaped polyethylene particles and the inorganicparticles within the above range, may secure cycle-life characteristicsand output characteristics of a battery.

The inorganic particles may include, for example, Al₂O₃, SiO₂, TiO₂,SnO₂, CeO₂, MgO, NiO, CaO, GaO, ZnO, ZrO₂, Y₂O₃, SrTiO₃, BaTiO₃,Mg(OH)₂, boehmite, or a combination thereof, but are not limitedthereto. Organic particles such as an acrylic compound, an imidecompound, an amide compound, or a combination thereof may be furtherincluded in addition to the inorganic particles, but are not limitedthereto.

The inorganic particles may be spherical, flake-shaped, cubic, oramorphous. The inorganic particles may have an average particle diameter(D50) of about 1 nm to about 2500 nm, for example about 100 nm to about2000 nm, about 200 nm to about 1500 nm, or about 300 nm to about 1500nm. The average particle diameter of the inorganic particle may be anaverage particle size (D₅₀) at a volume ratio of 50% in a cumulativesize-distribution curve.

The negative electrode functional layer may have a thickness of about 1μm to about 10 μm, and specifically about 3 μm to about 10 μm.

In addition, a ratio of the thickness of the negative active materiallayer to the thickness of the negative electrode functional layer may beabout 50:1 to about 10:1, and specifically about 30:1 to about 10:1.

The thickness of the negative electrode functional layer within theabove range, may significantly improve the thermal stability whilemaintaining excellent cycle-life characteristics.

In particular, the ratio of the thickness of the negative electrodefunctional layer in the above range, may improve thermal safety whileminimizing the decrease in energy density.

The negative current collector may include one selected from a copperfoil, a nickel foil, a stainless steel foil, a titanium foil, a nickelfoam, a copper foam, a polymer substrate coated with a conductive metal,and a combination thereof.

The negative active material may include a material that reversiblyintercalates/deintercalates lithium ions, a lithium metal, a lithiummetal alloy, a material capable of doping/dedoping lithium, or atransition metal oxide.

Examples of the material capable of reversiblyintercalating/deintercalating the lithium ions may include acarbonaceous material, that is, a carbon-based negative active materialgenerally used in a rechargeable lithium battery. Examples of thecarbon-based negative active material may be crystalline carbon,amorphous carbon, or a combination thereof. The crystalline carbon maybe graphite such as non-shaped, sheet-shaped, flake-shaped, sphericalshape, or fiber shaped natural graphite or artificial graphite, and theamorphous carbon may be a soft carbon, a hard carbon, a mesophase pitchcarbonization product, fired coke, and the like.

The lithium metal alloy includes an alloy of lithium and a metalselected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba,Ra, Ge, Al, and Sn.

The material capable of doping/dedoping lithium may be a silicon-basedor tin-based material, for example, Si, SiO_(x) (0<x<2), a Si-Q alloy(wherein Q is an element selected from an alkali metal, analkaline-earth metal, a Group 13 element, a Group 14 element, a Group 15element, a Group 16 element, a transition metal, a rare earth element,and a combination thereof, but not Si), a Si-carbon composite, Sn, SnO₂,a Sn—R alloy (wherein R is an element selected from an alkali metal, analkaline-earth metal, a Group 13 element, a Group 14 element, a Group 15element, a Group 16 element, a transition metal, a rare earth element,and a combination thereof, but not Sn), a Sn-carbon composite and thelike. At least one of these materials may be mixed with SiO₂. Theelements Q and R may be selected from Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr,Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs,Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb,Bi, S, Se, Te, Po, and a combination thereof.

The transition metal oxide may include a lithium titanium oxide.

In the negative active material layer, an amount of the negative activematerial is about 95 wt % to about 99 wt % based on a total weight ofthe negative active material layer.

The negative active material layer may optionally further include anegative electrode conductive material and a negative electrode binder.

Each amount of the negative electrode conductive material and negativeelectrode binder may be about 1 wt % to about 5 wt % based on a totalweight of the negative active material layer.

The negative electrode conductive material is used to impartconductivity to the negative electrode, and types of the negativeelectrode conductive material is the same as types of the positiveelectrode conductive material described above.

The negative electrode binder improves binding properties of negativeactive material particles with one another and with a current collector.The negative electrode binder may be a non-water-soluble binder, awater-soluble binder, an amphiphilic binder(water-soluble/non-water-soluble binder), or a combination thereof.

The non-water-soluble binder may be polyvinylchloride, carboxylatedpolyvinylchloride, polyvinylfluoride, an ethylene oxide-containingpolymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene,polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide,polyimide, or a combination thereof.

The water-soluble binder may be a styrene-butadiene rubber, an acrylatedstyrene-butadiene rubber, polyvinyl alcohol, sodium polyacrylate, acopolymer of propylene and a C₂ to C₈ olefin, a copolymer of(meth)acrylic acid and (meth)acrylic acid alkyl ester, or a combinationthereof.

The amphiphilic binder may be an acrylated styrene-based rubber.

When the water-soluble binder is used as a negative electrode binder, acellulose-based compound may be further used to provide viscosity as athickener. The cellulose-based compound includes one or more ofcarboxylmethyl cellulose, hydroxypropylmethyl cellulose, methylcellulose, or alkali metal salts thereof. The alkali metals may be Na,K, or Li. The thickener may be included in about 0.1 parts by weight toabout 3 parts by weight based on 100 parts by weight of the negativeactive material.

The rechargeable lithium battery according to an embodiment of thepresent disclosure simultaneously includes a positive active materiallayer including the first and second positive active materials alongwith the negative electrode functional layer including the flake-shapedpolyethylene particles and disposed on the negative electrode andaccordingly, may minimize the capacity deterioration and lower aheat-increasing rate due to thermal/physical impacts and thuseffectively exhibit a shut-down effect.

On the other hand, the separator 13 may be disposed between the positiveelectrode 11 and the negative electrode 12 as described above. Theseparator 13 may be, for example, selected from a glass fiber,polyester, polyethylene, polypropylene, polytetrafluoroethylene, or acombination thereof. It may have a form of a non-woven fabric or a wovenfabric. For example, in a rechargeable lithium battery, apolyolefin-based polymer separator such as polyethylene andpolypropylene is mainly used. In order to ensure the heat resistance ormechanical strength, a coated separator including a ceramic component ora polymer material may be used. Optionally, it may have a mono-layeredor multi-layered structure.

Hereinafter, the above aspects of the present disclosure are illustratedin more detail with reference to examples. However, these examples areexemplary, and the present disclosure is not limited thereto.

(Manufacture of Rechargeable Lithium Battery Cells)

EXAMPLE 1

95 wt % of a positive active material prepared by mixing LiCoO₂/LiFePO₄in a weight ratio of 9:1 as first/second positive active materials, 3 wt% of a polyvinylidene fluoride binder, and 2 wt % of a ketjen blackconductive material were mixed in an N-methylpyrrolidone solvent toprepare positive active material slurry. The positive active materialslurry was coated on an aluminum current collector and then, dried andcompressed to manufacture a positive electrode having a positive activematerial layer.

98 wt % of graphite, 0.8 wt % of carboxylmethyl cellulose, and 1.2 wt %of a styrene-butadiene rubber were mixed in pure water to preparenegative active material slurry. The negative active material slurry wascoated on both surfaces of a copper current collector and then, driedand compressed to manufacture a negative electrode having a negativeactive material layer.

48 wt % of 2 μm flake-shaped PE particles (a long axis length/a shortaxis length=about 2, a thickness=about 0.6 μm), 47 wt % of alumina (anaverage particle diameter (D50)=1.2 μm), and 5 wt % of an acrylatedstyrene-based rubber binder were mixed in an alcohol-based solvent toprepare PE/alumina slurry.

The PE/alumina slurry was coated on both of the surfaces of the negativeelectrode and then, dried and compressed to manufacture a negativeelectrode having a coating layer including the flake-shaped PEparticles.

The negative electrode/a separator/the positive electrode/a separatorwere laminated in order to form a jelly roll-shaped electrode laminate(L/W of an electrode laminate=2.3).

This jelly roll-shaped electrode laminate and an electrolyte (1.0 MLiPF₆ in EC/DEC=50:50 v/v) were put in a battery case and sealed tomanufacture a pouch cell.

EXAMPLE 2

A rechargeable lithium battery cell was manufactured according to thesame method as Example 1 except that L/W of the electrode laminate waschanged into 1.1.

COMPARATIVE EXAMPLE 1

A rechargeable lithium battery cell was manufactured according to thesame method as Example 1 except that L/W of the electrode laminate waschanged into 2.5.

COMPARATIVE EXAMPLE 2

A rechargeable lithium battery cell was manufactured according to thesame method as Example 1 except that L/W of the electrode laminate waschanged into 1.

Evaluation Example: Penetration Safety Evaluation

Each ten rechargeable battery cells according to Examples 1 and 2 andComparative Examples 1 and 2 were manufactured, and a penetration safetyevaluation thereof was performed.

The penetration safety evaluation was performed by charging therechargeable lithium battery cells of Examples 1 and 2 and ComparativeExamples 1 and 2 at 0.5 C and 4.3 V under a cut-off of 0.05 C and onehour later, penetrated with a pin having a diameter of 3 mm at 80Mm/sec, and the results are examined.

While the penetration safety evaluation was performed, a heat transfersimulation of the rechargeable lithium battery cells were conducted, andthe results are shown in FIGS. 3 and 4.

FIG. 3 shows heat transfer simulation results over time duringpenetration safety evaluation for the rechargeable lithium battery cellsaccording to Examples 1 and 2 of the present disclosure.

FIG. 4 shows heat transfer simulation results over time duringpenetration safety evaluation for the rechargeable lithium battery cellsaccording to Comparative Examples 1 and 2.

Referring to FIG. 3, in the rechargeable lithium battery cells havingL/W in a range of 1.1 to 2.3, the heat transfer was smoothly performedduring the penetration and led to an early shut-down beforeexplosion/ignition of the battery cells and thus might securepenetration safety.

On the contrary, referring to FIG. 4, in the rechargeable lithiumbattery cells having L/W of less than 1.1 or L/W of greater than 2.3,the heat transfer was not smoothly performed and might fail in leadingthe early shut-down and cause explosion/ignition of the battery cells.In other word, when L/W did not satisfy the range of 1.1 to 2.3, theheat transfer was not smoothly performed, and accordingly, safety wasnot secured.

On the other hand, the penetration safety evaluation results of therechargeable lithium battery cells of Examples 1 and 2 and ComparativeExamples 1 and 2 are shown in Table 1. In Table 1, the numbers refer tothe number of battery cells in which non-ignition, smoke generation, andignition occurred.

TABLE 1 L/W Non-ignition Smoke generation Ignition Example 1 2.3 10 0 0Example 2 1.1 10 0 0 Comparative 2.5 5 2 3 Example 1 Comparative 1.0 5 23 Example 2

As shown in Table 1, as for the battery cells of Examples 1 and 2 havinga length relative to width ratio (L/W) of an electrode laminate in arange of 1.1 to 2.3, the heat was transferred all over the electrodelaminate in the penetration test, thus securing excellent safety.

However, the battery cells of Comparative Examples 1 and 2 did notsatisfy L/W of 1.1 to 2.3 and hardly secured penetration safety andaccordingly, Examples 1 and 2 exhibited much excellent safety comparedwith the battery cells of Comparative Examples 1 and 2.

Although certain exemplary embodiments and implementations have beendescribed herein, other embodiments and modifications will be apparentfrom this description. Accordingly, the inventive concepts are notlimited to such embodiments, but rather to the broader scope of theappended claims and various obvious modifications and equivalentarrangements as would be apparent to a person of ordinary skill in theart.

What is claimed is:
 1. A rechargeable lithium battery, comprising: anelectrode laminate comprising: a positive electrode comprising: apositive current collector; and a positive active material layerdisposed on the positive current collector; a negative electrodecomprising: a negative current collector; a negative active materiallayer disposed on the negative current collector; and a negativeelectrode functional layer disposed on the negative active materiallayer; and a separator, wherein the electrode laminate has a ratio (L/W)of a height (L), which is a length in a protruding direction of theelectrode terminal, relative to a width (W), which is perpendicular tothe protruding direction of the electrode terminal and parallel to thelaminate surface, ranges between about 1.1 and about 2.3, wherein thepositive active material layer comprises: a first positive activematerial comprising at least one of a composite oxide of a metalselected from cobalt, manganese, nickel, and a combination thereof andlithium; and a second positive active material comprising a compoundrepresented by Chemical Formula 1, wherein the negative electrodefunctional layer comprises: flake-shaped polyethylene particles, andwherein an operation voltage is greater than or equal to about 4.3 V,Li_(a)Fe_(1-x1)M_(x1)PO₄   [Chemical Formula 1] wherein, 0.90≤a≤1.8,0≤x1≤0.7, and M is Mn, Co, Ni, or a combination thereof.
 2. Therechargeable lithium battery of claim 1, wherein the electrode laminatehas a volume of about 17.5 cc to about 30 cc.
 3. The rechargeablelithium battery of claim 1, wherein the electrode laminate has an energydensity of about 600 Wh/L to about 750 Wh/L.
 4. The rechargeable lithiumbattery of claim 1, wherein the operation voltage is about 4.3 V toabout 4.5 V.
 5. The rechargeable lithium battery of claim 1, wherein thefirst positive active material is included in about 80 wt % to about 97wt % based on a total weight of the positive active material layer. 6.The rechargeable lithium battery of claim 1, wherein the first positiveactive material and the second positive active material are included ina weight ratio of about 97:3 to about 80:20.
 7. The rechargeable lithiumbattery of claim 1, wherein the positive active material layer furthercomprises: a positive electrode functional layer disposed on thepositive active material layer.
 8. The rechargeable lithium battery ofclaim 7, wherein the first positive active material is included in thepositive active material layer, and the second positive active materialis included in at least one of the positive active material layer andthe positive electrode functional layer.
 9. The rechargeable lithiumbattery of claim 1, wherein the first positive active material comprisesone selected from LiCoO₂, Li_(b)M¹ _(1-y1-z1)M² _(y1)M³_(z1)O₂(0.9≤b≤1.8, 0≤y1≤1, 0≤z1≤1, 0≤y1+z1≤1, M¹, M², and M³ areindependently a metal of Ni, Co, Mn, Al, Sr, Mg, or La), and acombination thereof.
 10. The rechargeable lithium battery of claim 1,wherein the second positive active material comprises LiFePO₄.
 11. Therechargeable lithium battery of claim 1, wherein an average particlesize (D50) of the flake-shaped polyethylene particles is about 1 μm toabout 8 μm.
 12. The rechargeable lithium battery of claim 1, wherein aratio of the long axis length relative to the short axis length of theflake-shaped polyethylene particles is about 1 to about
 5. 13. Therechargeable lithium battery of claim 1, wherein a thickness of theflake-shaped polyethylene particles is about 0.2 μm about 4 μm.
 14. Therechargeable lithium battery of claim 1, wherein the negative electrodefunctional layer further comprises inorganic particles and a binder. 15.The rechargeable lithium battery of claim 14, wherein a sum weight ofthe flake-shaped polyethylene particles and the inorganic particles overa weight of the binder is about 80:20 to about 99:1 by weight.
 16. Therechargeable lithium battery of claim 14, wherein the flake-shapedpolyethylene particles and the inorganic particles are included in aweight ratio of about 95:5 to about 10:90.
 17. The rechargeable lithiumbattery of claim 1, wherein the negative electrode functional layer hasa thickness of about 1 μm to about 10 μm.